Automated install of SQL Express from commandline

setup.sql

# If you want to give owner access to the whole server to a particular user account this is how
exec sp_addrolemember 'db_owner', 'NT AUTHORITY\NETWORK SERVICE';
GO

# If you want to idempotently ensure a particular database with name DatabaseName exists this is how
IF NOT db_id('DatabaseName') IS NOT NULL BEGIN

    PRINT 'Creating database...'
    CREATE DATABASE [DatabaseName]
    PRINT 'Created database.'

END

GO

sqlexpress.psm1

function Install-SQLServerExpress2014AndManagementStudio() {
    if (-not (Test-Path "C:\Program Files\Microsoft SQL Server\MSSQL12.SQLEXPRESS")) {
        if (-not (Test-Path "C:\tempsql\SQLEXPRWT_x64_ENU.exe")) {
            Write-Output "Downloading SQL Server 2014 Express: this may take a while`r`n"
            mkdir c:\tempsql -Force
            (New-Object Net.WebClient).DownloadFile('http://download.microsoft.com/download/E/A/E/EAE6F7FC-767A-4038-A954-49B8B05D04EB/ExpressAndTools%2064BIT/SQLEXPRWT_x64_ENU.exe','C:\tempsql\SQLEXPRWT_x64_ENU.exe')
        }
        Write-Output "Unpacking SQL Server 2014 Express`r`n"
        C:\tempsql\SQLEXPRWT_x64_ENU.exe /x:"c:\tempsql\SQLEXPRWT_x64_ENU" /u | Out-Null
        Write-Output "Adding .NET 3.5`r`n"
        Import-Module Servermanager
        Add-WindowsFeature NET-Framework-Core
        Write-Output "Installing SQL Server 2014 Express: this may take a while`r`n"
        C:\tempsql\SQLEXPRWT_x64_ENU\setup.exe /QUIETSIMPLE /ACTION=install /FEATURES=SQL,Tools /IAcceptSQLServerLicenseTerms /INSTANCENAME="SQLExpress"
        $env:PATH = [System.Environment]::GetEnvironmentVariable("Path","Machine")
        Remove-Item -Recurse -Force c:\tempsql
    } else {
        Write-Output "SQL Server 2014 Express already installed`r`n"
    }
}

usage.ps1

Import-Module (Join-Path $PSScriptRoot sqlexpress.psm1) -Force
Install-SQLServerExpress2014AndManagementStudio
& sqlcmd -S ".\SQLEXPRESS" -E -i "$PsScriptRoot\setup.sql"

Alternatively, you can use this which doesn't also install management studio (and the download drops from over 800MB to just under 200MB so the install is a lot faster):

function Install-SQLServerExpress2014() {
    if (-not (Test-Path "C:\Program Files\Microsoft SQL Server\MSSQL12.SQLEXPRESS")) {
        if (-not (Test-Path "C:\tempsql\SQLEXPR_x64_ENU.exe")) {
            Write-Output "Downloading SQL Server 2014 Express: this may take a while`r`n"
            mkdir c:\tempsql -Force
            (New-Object Net.WebClient).DownloadFile('http://care.dlservice.microsoft.com/dl/download/E/A/E/EAE6F7FC-767A-4038-A954-49B8B05D04EB/Express%2064BIT/SQLEXPR_x64_ENU.exe', 'c:\tempsql\SQLEXPR_x64_ENU.exe')
        }
        Write-Output "Unpacking SQL Server 2014 Express`r`n"
        C:\tempsql\SQLEXPR_x64_ENU.exe /x:"c:\tempsql\SQLEXPR_x64_ENU" /u | Out-Null
        Write-Output "Adding .NET 3.5`r`n"
        Import-Module Servermanager
        Add-WindowsFeature NET-Framework-Core
        Write-Output "Installing SQL Server 2014 Express: this may take a while`r`n"
        C:\tempsql\SQLEXPR_x64_ENU\setup.exe /QUIETSIMPLE /ACTION=install /FEATURES=SQL /IAcceptSQLServerLicenseTerms /INSTANCENAME="SQLExpress"
        $env:PATH = [System.Environment]::GetEnvironmentVariable("Path","Machine")
        Remove-Item -Recurse -Force c:\tempsql
    } else {
        Write-Output "SQL Server 2014 Express already installed`r`n"
    }
}